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Table 2 Number of breast cancers, person-years, rates, and RRs by demographic, reproductive, and anthropometric factors.

From: Breast cancer epidemiology according to recognized breast cancer risk factors in the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial Cohort

  Breast Cancers* Woman-Years Crude Rate RR** 95% CI
Attained Age      
   55–59 274 63,088 434.31 1.00 Ref.
   60–64 608 108,640 559.65 1.36 1.18–1.57
   65–69 582 104,433 557.30 1.44 1.24–1.67
   70–74 434 79,134 548.44 1.48 1.26–1.73
   75+ 187 34,419 543.30 1.47 1.21–1.79
Race      
   White 1,854 345,926 535.95 1.00 Ref.
   African-American 89 19,765 450.29 1.05 0.84–1.32
   Asian/Pacific Islander 111 17,230 644.23 1.14 0.86–1.51
   Other/unknown 31 6,793 456.35 0.92 0.64–1.32
Family history of breast cancer      
   No 1696 336,410 504.15 1.00 Ref.
   Yes 389 53,304 729.78 1.44 1.29–1.60
Number of Live Births      
   0 240 35,545 675.20 1.00 Ref.
   1 160 28,296 565.45 0.70 0.55–0.89
   2 524 88,510 592.02 0.76 0.62–0.92
   3 526 96,163 546.99 0.75 0.62–0.91
   4 331 66,673 496.45 0.72 0.59–0.88
   5+ 301 73,888 407.37 0.65 0.53–0.80
Age at First Birth      
   None 240 35,545 675.20 1.00 Ref.
   < 20 267 62,165 429.50 0.68 0.53–0.86
   20–24 901 181,709 495.85 0.74 0.59–0.91
   25–29 471 80,523 584.93 0.83 0.66–1.03
   30–34 148 20,822 710.79 1.03 0.81–1.31
   35+ 47 6,894 681.75 1.02 0.74–1.41
Age at Menarche      
   < 12 years 457 76,987 593.61 1.00 Ref.
   12–13 years 1099 209,082 525.63 0.86 0.77–0.97
   14–15 years 439 84,595 518.94 0.85 0.74–0.97
   ≥ 16 years 88 17,874 492.34 0.81 0.65–1.02
Age at Menopause      
   < 45 years 123 25,254 487.05 1.00 Ref.
   45–49 years 340 64,113 530.31 1.07 0.87–1.31
   50–54 years 700 126,080 555.20 1.12 0.92–1.35
   55+ years 211 32,192 655.44 1.29 1.03–1.62
   Surgical menopause 574 122,386 469.01 0.84 0.69–1.02
   Radiation/medication 94 12,061 779.37 1.32 1.01–1.74
Menopausal hormone therapy use      
   Never 571 134,329 425.08 1.00 Ref.
   Former 280 64,773 432.28 1.02 0.88–1.18
   Current, < 5 years 372 61,931 600.67 1.44 1.26–1.66
   Current, ≥ 5 years 847 125,006 677.57 1.67 1.49–1.87
Weight (kg)      
   < 60 437 82,961 526.75 1.00 Ref.
   60 – 64.9 310 59,068 524.82 1.03 0.86–1.19
   65 – 69.9 311 56,091 554.46 1.18 0.97–1.30
   70 – 74.9 257 49,325 521.03 1.08 0.92–1.26
   75 – 79.9 267 47,072 567.22 1.21 1.03–1.42
   ≥ 80 486 91,892 528.88 1.20 1.04–1.38
Height (m)      
   < 1.60 527 101,460 519.42 1.00 Ref.
   1.60 – 1.64 605 117,236 516.05 1.01 0.89–1.13
   1.65 – 1.69 561 102,205 548.90 1.06 0.94–1.20
   ≥ 1.70 385 66,707 577.15 1.11 0.97–1.27
BMI (kg/m2)      
   < 18.5 25 5,135 486.85 0.88 0.59–1.32
   18.5 – 24.9 848 154,447 549.06 1.00 Ref.
   25 – 29 712 133,799 532.14 1.06 0.95–1.17
   30 – 34.9 305 59,109 516.00 1.10 0.97–1.26
   ≥ 35 173 32,478 532.67 1.21 1.02–1.43
  1. * Includes confirmed invasive cancers, confirmed in situ lesions, and self-reported cancers.
  2. ** Adjusted for attained age, screening center, age at menarche, age at menopause, family history of breast cancer, benign breast disease, height, and menopausal hormone therapy (all in categories as shown in the table), plus combined age at first birth and parity (nulliparous or first birth after 35 years, first birth before age 25, first birth 25–34 years, or unknown) and calendar time (5/31/1993 – 5/31/1995, 6/1/1995 – 5/31/1997, 6/1/1997 – 5/31/1999, 6/1/1999 – 5/31/2001, and 6/1/2001 – 5/31/2003). RRs for age at first birth and parity were adjusted for the other factor.
  3. Not shown are unknown parity (3 breast cancers and 638 person-years), age at first birth (11 breast cancers and 2,635 person-years), age at menarche (2 breast cancers and 1,177 person-years), age at or type of menopause (43 breast cancers and 7,628 person-years), menopausal hormone therapy use (15 breast cancers and 3,676 person-years), weight (17 breast cancers and 3,304 person-years), height (7 breast cancers and 2,107 person-years), and BMI (22 breast cancers and 4,747 person-years).